Wal-Mart workers and union activists protest outside a Wal-Mart store on June 4, 2014 in Chicago.

"It's once again saying that labor unions are not wanted," said Michael Lotito, a labor management relations lawyer at the law firm Littler.

"We continue to see an erosion of unions and their ability to organize over the last 20 years or so," he added. "It's definitely a setback for public sector unions."

The case, Harris v Quinn, involved in-home care workers that were paid by the state of Illinois.

Quinn refers to the current governor of Illinois, Democrat Pat Quinn.

'More lawsuits likely'

SCOTUS: Workers can't be forced to pay union fees

In a 5 to 4 decision the U.S. Supreme Court has ruled home care workers cannot be forced to pay union fees. CNBC's Hampton Pearson reports the details.

The plaintiffs wanted the court to overrule a 1977 decision, Abood v. Detroit Board of Education, which declared that government employees can be required to pay fees to unions for representing them and administering their contracts even if they disagree with the union's positions.

However, the court held on a 5-4 vote, that plaintiff Pamela Harris and others who provide in-home care for relatives and others with disabilities, were not full-fledged public employees and could not be forced to pay union dues to a public employees union they belonged to.

Gerry Berendt, a professor of labor law at John Marshall Law School, said he wasn't really surprised by Monday's ruling considering the conservative make-up of the court.

But he did see a bright spot for labor.

"The ruling was fairly narrow because it did not overturn Abood," Berendt argued. "That's some hope for unions, but not much.There will like be more lawsuits like this in the future challenging the issue of forced fees."

Future of unions?

Reaction was swift from both sides of the issue.

The Competitive Enterprise Institute, a policy group that believes in free enterprise and limited government, hailed the decision in an email as a "win for the first amendment" and a "blow to the coercive powers of government unions."

But the National Employment Law Project, a labor advocacy group said, said in an email to CNBC that "the court showed indifference to how labor-management relations can be properly and lawfully constructed to promote meaningful worker input into issues affecting their employment and the service they provide."